A few opportunities have come up for saving something with unknown availability for this gardener.
An annual brassica was one of these. I bought a package of seed off the rack in an Asian market, immediately forgotten was the name it was sold under. It isn't all that special but just a mild-flavored brassica. Buying seed for what I thought it is from 3 different seed companies has broadened my experience but hasn't eliminated the need to save seed from the un-duplicated original.
I found the annual brassicas easy choices for a casual seed-saver. My grandmother's tomato, from seed given me about 30 years ago, has been an easy save and not required isolation. Only once did it seem to cross with another variety. The experience made me aware of the value in saving seed from multiple years. No seed need be collected from the "suspect" plant(s). The "suspect" seed from the previous year can be tossed. And, older seed (not too much older!) can be used again. Worked!
Steve